1. Field of the Invention
The present invention relates to a lubricating device for an electric motor for use in an electric automobile.
2. Description of the Prior Art
In recent years, in view of environmental problems, electric automobiles have been extensively developed. One known type uses wheel motors with each motor being directly connected to a wheel through a reduction gear or mechanism.
In an arrangement wherein each wheel is directly connected to a motor through the reduction gear, it is necessary to prevent the vehicle body from interfering with the motor and the reduction gear during vertical movements and steering operations of the wheels. This requirement places a restriction on installation space. Therefore, reduction of the size of the motor and of the reduction gear is necessary to mount them in a limited space. Further, electric automobiles require motors which have a small and light structure as well as a large output torque so as to provide high power relative to the vehicle weight.
However, in order to reduce the size and weight of the motor and to increase the output torque thereof, it is necessary to pass a large current through the coil of the motor, so that the coil generates a large amount of heat, which heat may cause burning of the coil. Therefore, it is important to suppress the heating of the coil in the overloaded state, by cooling it in order to obtain the intended performance of the motor.
FIG. 3 illustrates an example of a cooling device for the wheel motor which has been proposed by the applicant.
A casing assembly or main part 81 fixedly supports a stator 83 around which a coil is wound. In the casing assembly 81, a rotor 82 is supported by bearings, and a reduction gear or mechanism 96 is arranged to transmit rotation of the rotor to an output shaft 97. The rotation of the rotor is detected by a resolver 95. An oil pump 86 is disposed at a lower portion of the casing assembly, and a plate 87 and a cover 88 provided with fins are formed on a side wall of the casing to form an oil passage 89 which has an inlet port 90 at its lower end and an outlet port 91 at its upper end. The outlet port 91 is in communication with an oil passage 92 located at an upper end of the casing. The oil passage 92 has a discharge port 93.
Cooling oil is supplied by the oil pump 86 from an oil sump 85 through the inlet port 90 into the oil passage 89 and is cooled while it flows upward in the oil passage 89. The cooled oil is introduced through the outlet port 91 into the oil passage 92, and is ejected through the discharge port 93 directly onto the stator coil 84 to cool it. The oil which has received heat from the coil returns to the oil sump along an oil guide 94, flowing over a coil end.
Lubrication of the reduction gear and other elements is effected by oil which overflows directly onto them from the oil guide, or by the oil which is thrown from the peripheral surfaces of the rotating rotors, in other words, by centrifugal force.
However, the oil is required to perform several functions, i.e. the cooling function for removing heat from the coil, the function of reducing friction at friction surfaces of the reduction mechanism, and the function of removing the frictional heat. Therefore, oil having a low viscosity has been used to increase the cooling effect on the coil and the reduction mechanism. However, such oil may not form a stable oil film when it is heated by the hot coil, so that the effectiveness for reducing the friction of the reduction gear is decreased and the durability of the reduction gear and moving components is adversely affected.
It is an object of the invention to provide a lubricating device for a wheel motor, overcoming the above-noted problems, in which both the cooling and the lubricating of the wheel motor can be effectively performed.